1. Field of the Invention
The present invention relates to an electrode for a storage battery and a method for manufacturing the electrode for a storage battery.
2. Description of the Related Art
With the recent rapid spread of portable electronic devices such as mobile phones, smartphones, electronic books, and portable game machines, secondary batteries for drive power supply have been increasingly required to be smaller and to have higher capacity. Storage batteries typified by lithium-ion secondary batteries, which have advantages such as high energy density and high capacity, have been widely used as secondary batteries used for portable electronic devices.
A lithium-ion secondary battery, which is one of storage batteries and widely used due to its high energy density, includes a positive electrode including an active material such as lithium cobalt oxide (LiCoO2) or lithium iron phosphate (LiFePO4), a negative electrode formed of a carbon material such as graphite capable of reception and release of lithium ions, a nonaqueous electrolyte in which an electrolyte formed of a lithium salt such as LiBF4 or LiPF6 is dissolved in an organic solvent such as ethylene carbonate (EC) or diethyl carbonate (DEC), and the like. A lithium-ion secondary battery is charged and discharged in such a way that lithium ions in the secondary battery are transferred between the positive electrode and the negative electrode through the nonaqueous electrolyte and intercalated into or deintercalated from the active materials of the positive electrode and the negative electrode.
A binder is mixed into the positive electrode or the negative electrode in order that active materials can be bound or an active material and a current collector can be bound. Since the binder is generally an organic high molecular compound such as polyvinylidene fluoride (PVDF) which has an insulating property, the electric conductivity of the binder is extremely low. Therefore, as the ratio of the mixed binder to the active material is increased, the amount of the active material in the electrode is relatively decreased, resulting in the lower discharge capacity of the secondary battery.
Hence, by mixture of a conductive additive such as acetylene black (AB) or graphite particles, the electric conductivity between active materials or between an active material and a current collector can be improved. Thus, a positive electrode active material with high electric conductivity can be provided (see Patent Document 1).